(sense
1): Interjection signifying
pain, weariness, disgust, resignation, etc. Very often part of oy vey or oy vas
mir. Compare to English Jeez. (from Yiddish "oy", probably from old
German; probably cognate to English "oh").
(sense 2): Interjection signifying annoyance. Very similar to sense 1, but more annoyed than resigned. (Probably from Cockney accent of English "Hey".)
(sense 3) Greeting meaning "hello" or "Hi". (Probably from Cockney "hi").